Attentional performance has been shown to be highly heritable in normal populations. This study seeks to identify genetic factors that underlie the high heritability of attentional performance among normal subjects through the use of highly specific and well-characterized chronometric, neuropsychological tasks. The tasks measure the efficiency of altering, orienting and executive attention network function and have been well characterized by functional imaging methods. A population-based gene association study using a collection of 30 candidate gene polymorphism previously implicated in attentional function and/or disorders involving attention will be used. Associations between attentional performance and genotype in normal subjects will validate the use of these specific endophenotypic measures for use in future genetic studies.